One week in January, a rare event occurred: A Friday and Saturday night passed with no sign of Crowley.

An entire week passed and J still hadn’t heard from his brother.

“Then a group of us got an email that said, ‘Hey guys, I built this, what do you think?’ It was the first version of Foursquare; it was originally called Jimmy Disco,” says J.

Today, Foursquare has 100 employees, more than 15 million users, and a valuation of $600 million.

But Foursquare wasn’t always smooth sailing for Crowley.

“Everyone thinks the Foursquare experience is this rocket ship that started at SXSW 2009 and it hasn't let up, when in reality it was a little spike and then a summer of nothing,” says Crowley.

It took him and Selvadurai about nine months to raise the first round of capital for Foursquare.

“Then it spiked back up and it plateaued, and it spiked back up and it plateaued,” he says. “Of course if you average it out [the Foursquare experience] looks like a nice hockey stick curve. If you zoom in a little bit it is super, super rocky.”

The rollercoaster that is Foursquare is a good analogy for Crowley’s life.

“My whole career is a bunch of sizzles and spikes,” says Crowley. “I'm still trying to make sense of all of it, but when you look back it all starts to connect. Everything connects in hindsight. Of course you don't realize any of that going forward, you only realize that when you look back.”

In many ways, Crowley is still the same shaggy-haired socializer he was in college. He still looks to make every situation more fun — last month he traveled across the country with five ridiculous-looking corn cob pipes to surprise his friends in Lake Tahoe.

"I hope he stays the way he is and doesn't grow up," says J. "He's about to turn 36 but Dennis hasn't slowed down to me. He is somehow able to keep that energy."

J's favorite moment with his brother? Winning Family Feud. "I think I got a bloody nose from us flailing around and cheering when we won Fast Money!" J recalls

As a business person, Crowley has grown up quite a bit. Foursquare has had opportunities to get acquired, but Crowley wants to keep control of his company this time around.

He has learned to strike a balance between fun and business although the two often overlap.

Crowley says he can be "a little bit of a hard-ass;" pushing people to create better experiences than they thought possible.

For Crowley, the quest to make life one big, social game may never be complete.

“Someone introduced me the other day as a serial entrepreneur and I don't see it that way at all," he says.

"I've been trying to solve the same problems for many years and build software that helps optimize downtime. Of course the problem set keeps evolving and changing."

Perhaps Crowley’s life-long wrestle with Foursquare stems from the fact that he so deeply embodies the product. Life, for him, is a constant game of checking in with people he loves. The personal reward he gets from being with friends and discovering new ways to have fun is what he wants every Foursquare user to experience.

At one point in our long interview, Crowley said: “I don't socialize more than the average person — maybe I do maybe I don't."

Told he almost certainly does, Crowley smiled and asked: “What do people normally do after work?

"Do people just go home? I feel like there's almost wasted time when you're not enjoying things with friends."